Asymmetrical cold cathode flip-flop circuit



C. R. WILLIAMS ETAL.

ASYMMETRICAL COLD CATHODE FLIP-FLOP CIRCUIT Filed June l2, 1950 Patented Apr. 15, `1952 UNITED ASYMMETRICAL COLD CATHODE FLIP-FLOP CIRCUIT Charles R. Williams, Hawthorne, and Glenn E.

Hagen, Lawndale, Calif., assignors to Northrop Aircraft, Inc., Hawtho of California rne, Calif., a corporation Application June 12, 1950, Serial No. 167,572

6 Claims. (Cl. 315-337) The present invention relates to cold cathode .tube flip-flop circuits suitable for use in binary counters, and is an improvement on the flipviiop circuit shown, described, and claimed in the `copending Hagen application, Serial No, 100,178,

led June 20, 1949, now Patent No. 2,575,559.

The term flip-nip as used herein defines a de- Vice which has two stable states and is capable of being triggered from one state to the other. A dual cold cathode gas tube flip-nop has two conductingstable states; either one cathode is conducting, or the other cathode is conducting. The tube is non-conducting only during relatively short transition times, and sufficient supply voltage is provided to insure reignition. Circuits for use with dual cathode gas tubes to obtain flip-flop operation thereof have the following requirements broadly in common:

1. A supply voltage source higher than the firing voltage of the tube.

2. A current limiting resistance in series with the supply voltage.

3. A cathode circuit such that in either stable state the on cathode is at a higher positive potential than the off cathode.

4. A means of coupling in a triggering pulse which decreases the voltage across the tube and extinguishes the glow current.

5. A means of maintaining the on to off -cathode differential voltage during the trigger- Aing transition time.

6. A means of delaying the rise of the voltage across the tube during triggering to allow ionization dissipation before reiiring.

One form in which these components can be combined is shown, described, and claimed in the Hagen application cited above.

The fundamental Hagen circuit is symmetrical land in mostinstances output can be taken from `one or the other of the cathodes, both such outputs being alike in Wave form. The voltage .output wave form on the cathodes is ideal for the control oi relays, gates and indicators, for example, but is not entirely suitable for diier lentiation to form the most desirable type of carry pulse when the circuit is used in multistage binary counters. The advantages of the asymmetrical circuit `of `the present invention over the symmetrical circuit are (1) all of the above six requirements can be satisfied with fewer circuit components; (2) the cathode voltage wave form, where its use is desired, is doubled in amplitude.

tpis an object of the present invention to" provide a modied Hagen circuit operative to provide a suitable carry pulse.

It is another object of the invention to provide a binary counter using asymmetrical flipflop circuits ofthe general Hagen type.

"It is still another object of the present inven-` 2 tion to provide a nip-nop circuit of the Hagen type having two distinct types of out-put wave forms available.

And it is a further objectof the present-invention to provide an asymmetrical flip-flop circuit of the general Hagen type.

' Brieiy, the present invention includes the use of a glow tube having an anode and two cathodes connected in a circuit where an input pulse will iiip the discharge from one cathode to the other. One cathode is connected to iire a two electrode glow tube, such as a neon indicator lamp, and the other cathode is connected to a resistance-capacity (RC) circuit, as in `the Hagen circuit described above.

During the nip-flop action of the circuit" 0f the present invention, a `sharp carry pulse is generated at one cathode as the two electrode glow tube connected thereto is fired, whereas a large, slower voltage swing can be obtained from the other cathode that is suitable for the control of relays, diode gates, etc.

The present invention will be more fully une derstood by reference to the drawings, in which:

4Figure 1 is a side View in elevation of a tube suitable for use in the circuit of the present invention.

Figure 2 is a diagram of one form of asymmetrical flip-flop according to the present invention.

Figure 3 is a diagram of a modification of the circuit of Figure 1.

Figure 4 is a binary counter circuit using one form of asymmetrical flip-nop circuit of the present invention.

As shown in Figure l, the tube preferred for use in all of the circuits of Figures 2 to 4 is provided with an envelope'l containing an anode Wire 2, flanked on each side by cathode wires 3 and 4. These wires pass through an external pinch 5 to form an anode lead 6 and cathode leads 1 and 8 respectively. i

A preferred tube is one inch long byfinch inside diameter. The gas pressurein the' tube, and the anode to cathode spacing is adjusted'to give a desirable firing to burning voltage differential. Electrode surface spacings of .030 inch in helium at 250 mm. Hg pressure are satisfactory, and cathode wires of .010 to .015 inch diameter, .1 inch long will satisfactorily carry up to 1.0 ma. current. Suitable tube currents for flip-flop operation range'from 0.1 to 1.0 ma. Such a tube Will provide usable on to .oi cathode differentials of from 50 to 150 volts;

. Burning voltages are about 150 to 200 `voltsv and ring potentials are about 250 to 500 volts depending upon gas mixture, and material and condition of cathodes. V For long life and most dependable operation, we prefer that the tube have fromone percent Y 3 to ve percent of a recombinable polyatomic gas therein, such as hydrogen or water vapor, for example, in addition to the inert gas lling, in

accordance with the teachings of another copending application, Serial No. 156,659, led April 18, 1950. The anode area is not critical, and conduction usually occurs from relatively small area points on the anode surface. The anode is preferably placed centrally between the two cathodes to obtain symmetrical electrical characteristics and in the same plane with the cathodes for ease of manufacture. However, in the circuits of Figures 2, 3 and 4, the anode 2 is shown as entering the tube from the opposite end of the envelope from the cathodes, for ease of circuit illustration.

Referring next to Figure 2, anode 2 is connected to a source 'I of positive potential greater than the striking voltage of the tube through a limiting resistor I0. Anode 2 is also connected to an input line ||Y through an input capacity I2, a diode I3 andl a pulse generator I4` generating negative input pulses. The diode I3 is ori- Y ented toV pass the negative pulses to the anode 2. Y

One cathode 4V is connected to the positive end of a constant voltage supply I5, and theother cathode 3 is connected to ground (and the negative end of source 1) through cathode resistor I6 paralleled by a cathoder capacity I1.

In the operation of the circuit of Figure 2, rst assume that there is a glow discharge between Y anode 2 and cathode 3. The. current of the discharge owing through limiting resistor Hl depresses the voltage of the source 'I suiciently that the voltage difference between vanode 2 and cathode 3 is only the burning voltage of the two. The current of the discharge flowing through cathode resistance IS causes condenser |`I to be charged to a. potential greater than supply voltage |5. If anegative pulse is applied at the anode 2 through the input diode I3 and condenser I2 combination, the glow discharge between anode 2 and cathode 3 will be. interrupted, and the voltage at anode 2 will then rise toward the -i-` value of source 'I. Before the voltage at anode 2 reaches the source value, there will be a glow discharge again initiated between anode 2 and one of the cathodes 3 and 4. The cathode condenser I'I, however, maintains the voltage at cathode 3 at a higher positive potential'than the voltage at cathode 4. Thus, the glow discharge will be struck between anode 2 and cathode 4.

, After the glow discharge has been initiated between cathode 4 and. anode 2, assume that another negative pulse is applied at anode 2 through theA input circuit I I. Again the glow discharge will be interrupted, and the rise of voltage at anode 2 toward the source voltage will be su-icient to restrike a glow discharge between ,anode 2 and cathodes 3 or 4. However, the condenser II is not charged, and the voltage at cathode 3 is lower than the voltage at cathode 4. Hence, the glow discharge will be struck between. cathode 3 and anode 2. The diode I3 permits negative pulses to pass relatively unimpeded from pulse- Vgenerator |14v to anode-2; yet prevents negative: pulses generated at anode 2, bythe restriking of the glow discharge, from being reilected backto pulse generator I4. During the "period of glow discharge,` when the potential of anode 2 is rising, diode |.3 is in its conducting state permitting input condenser I2 vto act to,v the-.full extent of itsy capacity. in controlling the anode 2 potential rise rate. of the rise rate obtains suicient glow discharge interruption time to permit necessary deionizetion of the gas before restriking. The diode I3 also acts as an anti-oscillation device to compensate for oscillatory tendencies caused by the anode to cathode capacitance loading effect of the connection of input condenser I2 from anode 2 through pulse generator |4 to ground. This speciic feature is shown described and claimed in our companion application, Serial No. 189,257, filed August 18, 1950.

In the modified circuit of Figure 3, the constant voltage source |5 is isolated from cathode 4 by a leak resistor 20,; and cathode 4 is connected to ground through a two electrode glow tube 2| and a second constant voltage source 22; the voltage difference between the two sources being of a value equal to or slightly less than the burning voltage of the two electrode glow tube 2|. The constant voltage source 22 is useful in adjusting the proper voltage to the two electrode glow tube 2|, but a two electrode glow tube 2| can be selected to have its burning voltage close to the voltage difference between cathode 4' and ground. In this case, the second constant voltage supply can be dispensed with, as shown by dotted line 23. A satisfactory two electrode glow tube suitable for use in the circuits of Figures 3 and 4 (to be described later) is type NE2, manufactured by the General Electric Company and well known in the art.

The general operation ofthe circuit of Figure 3 is very similar to that of the device of Figure 2. When cathode 3 is conducting, the current flow through cathode resistor I6 raises the potential of cathode 3 to a value X, for example. The voltage of constant voltage supply I5 is made to be approximately one-half the magnitude of X. Leakage resistor 20 maintains the potential of cathode 4 at the value one-half X when cathode 4 is not conducting glow current. Sharp output pulses are taken orf directly from cathode 4 through output line 24. These output pulses are positive pulses by nature of the` characteristics of the glow tube 2| and are generated by the rapid firing thereof.

f It is a well known property of gas and vapor tubes, in general, that very steep voltage wave fronts and high current pulses can be obtained from the ring of these tubes while under the stress of a high anode to cathode potential. Use is made of this property in the flip-flop tube I for the generation of carry' pulses. When the tube I is triggered "oiTl the plate potential rises, until the tube reres, to a valueA of approximately 400 volts above the lowest cathode. Upon ilring there is a very rapid drop in plate to onl cathode voltage accompanied by a relatively high cur'- rent surge through the tube. The carry pulses are derived from this voltage drop which may have a magnitude as high as 200 volts. Negative pulses can be coupled from the anode, or positive pulsesrcan be derived from the cathodes. Taking pulses from one of the cathodes automatically accomplishes the one-half input rate division required for binary counting carry pulses.

In the case of the two electrode glow tubev 2|, such as the type NEZ, the ring to burning potential drop is of the order of 20 volts if the voltage is applied relatively slowly (one millisecond). However,y if the voltage is applied rapidly (one microsecond), then ring potentials as high as volts can be obtained acrossl the two electrode glow tube 2|. The ring of the flip-flop tube This control supplies this rapid rise to a two electrode glow tube 2| in its cathode circuit. The firing of the two electrode glow tube 2| rapidly drops its potential to its burning voltage of about 50 volts. Hence, very sharp positive pulses as high as 100 volts in amplitude can be obtained across the two electrode glow tube 2|.

It should be noted further that even though the two electrode glow tube 2| is already conducting its exhibits considerable impedance to very sharp voltage changes. If constant supply voltage is sufficient to maintain conduction in the two electrode glow tube 2|, carry pulses will still be generated but they will be of diminished amplitude.

A second purpose of the glow tube 2| is that it indicates the binary state of the nip-flop and it indicates the total count of the binary counter.

A second output line 25 can be attached to cathode 3. This connection provides a wide but slow voltage swing suitable, as pointed out above, for thebiasing of diodes or other switching devices.

The diagram of Figure 4 shows the circuit of Figure 3 as connected in a binary counter, which may have as many stages as desired.

Here the output line 24 from cathode 4 is connected through the leakage resistor 20 and the constant voltage supply l5 to ground. The output line 24 is also connected through a differentiating capacity 30 connected through an inverting diode 3| to ground. The input line ||a of a second stage S is connected to the junction of capacity 3D and diode 3| In this circuit the pulses appearing in the output line 24 are positive and are bypassed through capacity 30 and diode 3| to ground, thereby charging condenser 30. When the positive pulse goes from its positive peak down to a normal voltage, the condenser 30 will tend to discharge through the now conducting two electrode glow tube 2 I, thereby establishing a negative pulse on the input diode |3a of the next stage S; this negative pulse being bypassed by input diode |3a to the anode of the next stage S, to trigger that stage.

As each stage of the binary counter shown in Figure 4 generates its own carry pulse, there is no limit to the number of stages that can be used. Further, the power consumption of each stage is very low so that the power consumption of a multi-stage binary counter is far lower than in the equivalent circuit using tubes that require cathode heating.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but

which obviously is susceptible of modication in its form, proportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute, the invention has been described in language more or less specic as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise the preferred form of several modes of putting the invention into effect, and the invention is, therefore, claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

What is claimed is:

l. A ilip-op circuit including a tube cornprising an envelope, a pair of cold cathodes and an intermediate anode'in said envelope, a filling of gas at glow discharge pressure in said envelope, a limiting resistance, a source of potential higher than the firing potential of said tube connected between said anode and both of said cathodes in series with said limiting resistance, an RC circuit connected to one of said cathodes, a constant voltage supply in series with the other `of said cathodes and subtractive to the potential of said source. and an input line connected to apply an input pulse to said anode.

Apparatus in accordance with claim 1 wherein a two electrode glow tube is directly connected between the cathode connected to said constant voltage supply and said source, wherein a leak resistor is connected between said constant voltage supply and said connected cathode, and an output line connected to said latter cathode, the potential of said constant voltage supply being approximately the burning potential of said two electrode glow tube.

3. A binary counter comprising a plurality of iiip-iiop stages, according to claim 2, with the output line of the one stage connected to the input line of the next stage through a pulse inversion means.

4. A binary counter comprising a plurality of flip-flop stages, according to claim 2, with the output line of one stage connected to the input line of the next stage through a pulse inversion means, said means including a series capacity and a rectifier across said output.

5. A flip-nop circuit including a tube comprising an envelope, a pair of cold cathodes and an intermediate anode in said envelope, a filling of gas at glow discharge pressure in said envelope, a limiting resistance, a source of potential higher than the tiring potential of said tube connected between said anode and both of said cathodes in f series with said limiting resistance, an RC circuit connected to one of said cathodes, a two electrode glow tube connected between said source and the other of said cathodes, an input line connected to apply an input pulse to said anode, and an output line connected to the last mentioned cathode.

6. A flip-nop circuit including a tube comprising an envelope, a pair of cold cathodes and an intermediate anode in said envelope, a fllling of gas at glow discharge pressure in said envelope,

a limiting resistance, a source of potential higher than the firing potential of said tube connected p. between said anode and both of said cathodes in vvseries with said limiting resistance, an RC cirfcuit connected to one of said cathodes, a two felectrode glow tube connected between said .source and the other of said cathodes, .an input line connected to apply an input pulse to said jmentioned cathode, said output `line including anode, and an output line connected to the last a pulse inversion network.

CHARLES R. WILLIAMS. GLENN E. HAGEN.

No references cited. 

